Pancake style motor/generators are so named because their general design provides for a relatively thin, circular rotor concentrically surrounded by a ring-like stator. For generator configurations, the rotor often uses permanent magnets and is not externally excited, while the stator comprises a series of externally-excited conductive windings.
The above arrangement makes pancake generators ideal in a mechanical sense for certain applications, such as in wind turbine nacelles. In such applications, the pancake generator mounts axially along the wind-driven shaft, such that the rotor and shaft rotate together.
The electrical machine shown in WO 2005/124967 A1 (2005-12-29) provides a structural example, which may be regarded as a type of pancake construction. In the '967 publication, one sees a circumferential ring stator surrounding the perimeter of a disc-shaped rotor. The '967 publication refers to this arrangement as an “axial flux” machine, and that terminology often (but not always) is used to describe pancake style motor/generator arrangements. Other terms that are sometimes used to describe pancake style motor/generators include “toroidal motor/generators,” where “toroidal” generally denotes the toroid-shaped stator structure positioned concentrically around a generally circular rotor (or rotor arms).
In any case, the general structure of pancake style motor/generators offers a number of design advantages, along with numerous challenges. For example, pancake style motor/generator construction poses a number of particular design challenges, in which the designer must balance the competing considerations of size, performance, power, and manufacturability/serviceability.
Of course, those skilled in the art will recognize that the particular design and construction details will depend on the targeted application. For various design approaches targeting a number of applications, see the following patent publications: US20090140526A1 (2009-06-04), US20090218895A1 (2009-09-03), EP1647081B1 (2008-03-26), WO2008014584A1 (2008-02-07), W02008116463A1 (2008-10-02), WO200811646A2 (2008-10-02), and KR2009084551A (2009-08-05). From among these examples, and others, one begins to appreciate the range of design choices involved in optimizing the performance, manufacturability, and cost of a pancake motor/generator, for a particular use.